Method and apparatus for machining both sides of workpieces

ABSTRACT

In a method and a multiple-spindle automatic lathe for machining both sides of workpieces, in order to increase the number of spindle positions available for machining the workpieces, it is suggested that the spindle drum be indexed in single steps, that the feeding of raw workpieces, the removal of finished workpieces and the changeover of half-finished workpieces be carried out in a single spindle position of the spindle drum and that the feeding of raw workpieces and the removal of finished workpieces occur alternately after each drum indexing.

This application is a continuation of application Ser. No. 07/221,456,filed June 3, 1988, now U.S. Pat. No. 5,020,402.

The invention relates to a method for machining both sides ofworkpieces, in which the workpieces are successively clamped in firstand second spindles on a first or a second side, respectively, on aspindle drum comprising several spindles, in particular, with spindleaxes which are parallel to each other and are arranged at equal angularspacings around a drum axis, and in which raw workpieces are fed to thefirst spindles, finished workpieces are removed from the secondspindles, and half-finished workpieces are changed over from the firstto the second spindles, with clamping of the workpieces beingsimultaneously changed from the first to the second side. The inventionfurther relates to a multiple-spindle automatic lathe for machining bothsides of workpieces with a spindle drum which comprises several spindlesand on which successive first and second spindles are provided forclamping the workpieces on a first or second side, respectively, with afeeding means for raw workpieces, with a conveying away means forfinished workpieces, with a workpiece gripping device and with aworkpiece holding device which is associated with the workpiece grippingdevice and which together with the workpiece gripping device forms ahandling unit for changing over the half-finished workpiece from thefirst to the second spindle, with the clamping of the workpiece beingsimultaneously changed from the first to the second side.

The machining of a turned part on a first and a second side, i.e., inparticular, a front and a rear side, in a machining cycle is alreadyknown in multiple-spindle automatic lathes. The Gildemeister publicationGM 030 3 Bu 1076 d describes on page 40 a six-spindle automatic lathewith a spindle drum in which three successive spindle positions are usedfor machining the front side of a chucked part and three furthersuccessive spindle positions for machining a rear side. Herein themachining of the chucked parts is to be carried out in such a way thatthe chucked parts are inserted in one spindle position into the spindledrum, then first pass through the three spindle positions for machiningthe front side, are subsequently changed over prior to machining of therear side, then pass through the three spindle positions for machiningthe rear side and finally after completion of machining of the rear sideare conveyed away as finished parts.

Herein the feeding means for raw workpieces is associated with the firstspindle position for machining the front side of the chucked parts soraw workpieces are always inserted into the spindles standing in thisspindle position and are clamped by these spindles on their first side.By indexing spindle drum one spindle position or one step, in each case,the inserted raw workpieces with the spindles clamping them pass throughall three spindle positions for machining the front side. Prior tomachining the rear side, the workpieces are to be changed over in such away that they are clamped on the second side. This is possible either inthe last spindle position for machining the front side or in the firstspindle position for machining the rear side. To this end, theworkpieces are removed from the spindle clamping them on their rearside, reversed and put back into the same spindle which must now clampthe workpieces on their front side which has already been machined.After passing through the three spindle positions for machining the rearside, the finished workpieces are transferred in the last spindleposition for machining the rear side to the conveying away means for thefinished workpieces.

In this apparatus described above, the spindles can only be equippedwith such clamping means as allow simultaneous clamping of the chuckedparts on the front and on the rear side. This may cause difficultieseven with conventional parts as it is not always possible to clamp apart both on the first side and on the second side with the sameclamping means.

Also, there is only a small number of spindle positions available formachining the workpieces since one spindle position for feeding rawworkpieces, one spindle position for conveying away finished workpiecesand one spindle position for reversing the parts usually have to beprovided. In particular, the spindle positions for feeding and conveyingaway the workpieces are usually not available for machining. Therefore,at the most two spindle positions are left for machining each workpieceside, and reversal of the workpiece also has to be carried out in one ofthese spindle positions.

Also described in the Gildemeister publication GM 030 3 Bu 1076 d, page40, is a second possibility for machining a workpiece on a first and asecond side, but with an eight-spindle lathe. Herein, the eight spindlesare likewise arranged on a spindle drum, and the individual spindles arenumbered 1 to 8 in accordance with their order. Spindles 1, 3, 5 and 7are provided for machining the front side and hence are also equippedwith suitable clamping means for clamping the workpiece on the rearside. The even-numbered spindles 2, 4, 6 and 8 are provided formachining the rear side and are equipped with suitable clamping meansfor clamping the workpieces on the front side. Hence the workpieces aresuccessively clamped on the spindle drum alternately with either theirfront side or their rear side so the respective other side is availablefor machining. A total of eight spindle stations fixed on the housingare associated with this spindle drum. In the described method, thespindle drum is indexed one double step, in each case, so only thespindles characterized by an even number pass only the spindle stationsbearing an even number, whereas the spindles bearing an uneven number,in turn, pass only spindle stations bearing uneven numbers. Two adjacentspindle stations are used to feed the raw workpieces and convey away thefinished workpieces and to simultaneously change over by means of areversing device the half-finished workpieces from the even-numbered tothe uneven-numbered spindles or vice versa.

Accordingly, with such an automatic multiple-spindle lathe, raw partsare, for example, inserted, in each case, into the uneven-numberedspindles in spindle position 1 and in a one-time machining cycle withdouble-step indexing are machined, in each case, in spindle positions 3,5 and 7 and arrive again as half-finished parts in spindle position 1.There, at the same time as a new raw part is inserted into this spindle,they are changed over by means of a reversing device to the adjacentspindle standing, for example, in spindle position 2 and in this spindlepass through all even-numbered spindle positions 4, 6 and 8 so as toarrive again as finished parts in spindle position 2 and be conveyedaway from there.

In this method, after each double-indexing step, before the next one, afinished part is removed from a spindle standing in spindle position 2,a half-finished part removed from the spindle standing in spindleposition 1, fed to the reversing device, a half-finished part removedfrom the latter and inserted into the spindle standing in spindleposition 2 and, finally, a raw part fed to the spindle standing inspindle position 1.

The advantage of this method and this apparatus is to be seen in thefact that each spindle has only to clamp the workpiece on the front orthe rear side and hence can be equipped with a suitable clamping means.However, there still remains the problem that on account of thedouble-step indexing, only half of the spindle positions is available,in each case, for machining the front side or for machining the rearside, and one spindle position is usually reserved, in each case, forthe feeding, conveying away and changing over devices. Hence with theeight-spindle lathe, only three spindle positions are available, in eachcase, for the front and rear side machining. There is the furtherdifficulty that on account of the spindle positions being adjacent toone another, handling of the workpieces is impeded as it is extremelydifficult to arrange a feeding means for raw parts, a conveying awaymeans for finished parts and also a reversing and changing over devicewhen two spindle positions are located adjacent to each other.

The object underlying the invention is, therefore, to so improve amethod of the generic kind that the number of spindle positionsavailable for machining the workpieces is increased.

This object is accomplished, in accordance with the invention, in amethod of the kind described at the beginning by the spindle drum beingindexed in single steps and by at least one first spindle position ofthe spindle drum being provided in which both the feeding of rawworkpieces, the removal of finished workpieces and the changing over ofhalf-finished workpieces is carried out in one single spindle positionof the spindle drum and in which the feeding of raw workpieces and theremoval of finished workpieces occur alternately after each drumindexing.

The inventive solution simultaneously offers several advantages. Onlyone spindle position is required for feeding, conveying away andchanging over the workpieces, which, therefore, already increases thenumber of spindle positions available for machining the workpiece.Furthermore, owing to only one access to a spindle position beingrequired, the handling device may be of simple and compact design, whichwith respect to the multiple-spindle automatic lathes known from theprior art with several feeding, conveying away and changing overdevices, results in a noticeably simpler design and also a substantiallysimplified control of the automatic lathe. Also, the number of spindlepositions available for each workpiece is more than doubled since eachworkpiece passes each spindle position and can, therefore, also bemachined in each spindle position. For example, with a six-spindle latheoperating according to the inventive method, the raw part can bemachined in at least five spindle positions until it arrives again inthe sixth spindle position from which it is changed over from the firstspindle to one of the second spindles and similarly passes through fivespindle positions again in which machining is possible. For reasons ofclarification only, reference is made again at this point to the methodsaccording to the prior art in which only half of the spindle positionsis available for machining the front or rear side, whether, as in thefirst case, front side machining be carried out in the first threespindle positions and rear side machining in the second three spindlepositions or double-step indexing be used, in which case each spindleposition is approached by either the first spindles or the secondspindles. In addition to this, there are the further disadvantages ofthe prior art which result from at least two spindle positions usuallybeing blocked by a feeding and a conveying away device. In the case of asix-spindle lathe, this usually leads to only two spindle positionsbeing available for machining the front side and two spindle positionsfor machining the rear side. This increase in the number of spindlepositions available for machining a workpiece is highly advantageous,above all, in the case of complex parts on which a large number ofmachining steps have to be carried out since the number of machiningtools which can be associated with a spindle position, for space reasonsalone, cannot be indefinitely increased, and so normally a maximum ofthree tools which are movable independently of one another can beassociated with each spindle position. Hence with the inventivesolution, a maximum of five times three, in each case, i.e., fifteentools can be used for machining the front and rear side, whereas in themethods according to the prior art, it is a maximum of two times three,in each case, i.e., six tools.

Finally, a further achievement made with the inventive method is thatonly workpieces can be inserted with their first side into the firstspindles and only workpieces with their second side into the secondspindles so the respective clamping means can be adapted to the firstand second sides of the workpieces.

The above-described method is--as already explained at thebeginning--superior, in particular, when workpieces are to be machinedwhich require a plurality of machining steps. In the machining of"simpler" workpieces, i.e., such as require less machining steps, theinventive method would not be used in an optimal manner. For thisreason, provision is made in a further embodiment of the inventivemethod for at least one second spindle position of the spindle drum tobe selected in which both additional feeding of raw workpieces,additional removal of finished workpieces and additional changing overof half-finished workpieces is carried out and in which the feeding ofraw workpieces and the removal of finished workpieces are carried outalternately after each drum indexing. In this way, optimal use is alsomade of the possibilities offered by the inventive method with the"simpler" workpieces and so with these simple workpieces approximately adoubling of the piece numbers is possible as compared with the firstembodiment.

The two spindle positions according to the further embodiment can beadvantageously selected in accordance with the number of machiningstations required for the workpieces and the further workpieces. In thesimplest case, these are so selected that they lie on opposite sides ofthe spindle drum, i.e., in particular, in mirror-image relation withrespect to an axis of rotation of the spindle drum.

In the above-described methods, it was not specified how the changeoverof a workpiece from the first to the second spindles and hence also thechange in the clamping from the first side to the second side are to becarried out. One skilled in the art is familiar with a large number ofmeasures for this purpose. The simplest changeover possibility is forthe changing over to include several transferrals of the workpiece,i.e., for the workpiece arriving on a first spindle in the spindleposition provided for the changeover to be transferred to severalworkpiece gripping devices until the second side of this workpiece canafter indexing of the spindle drum be clamped by a second spindlearriving in the spindle position provided for the changeover.

So long as the changeover includes only transferral of the workpiecewithout reversal of a workpiece holding device, i.e., when chuck-type orend face grippers are used as grippers, it is necessary for thechangeover to include an uneven number of transferrals of the workpiece,in which case the workpiece is gripped on the opposite side duringtransferral. Due to the uneven number of transferral steps, the clampingof the workpiece is automatically changed from the first to the secondside.

Instead of the uneven-numbered transferral during changeover, it is,however, similarly possible for the changeover to include reversal. Inthis case, it is no longer necessary for an uneven number oftransferrals to be carried out. Here, it is conceivable to provide, forexample, a separate reversing device, or a radial gripper for reversingthe workpiece may also be provided on the workpiece gripping device.

In order to lose as little time as possible during changeover, it isadvantageous for the changeover to be carried out in a working area ofthe machine tool so as to move the workpiece over distances which are asshort as possible and thereby save as much time as possible.

On the other hand, it may be avantageous, if, for example, a machiningstep is also to be carried out in the spindle position provided for thechangeover, for the reversing to be carried out outside of the workingarea in order to prevent contamination of the workpiece by chips.However, this may also prove necessary if chips occurring in the workingarea are difficult to remove from the workpiece and a chip should, underno circumstances, be clamped in when clamping on the second side iseffected. With this type of procedure, it is, for example, also possibleto clean the workpiece thoroughly during reversal outside of the workingarea.

Within the scope of the above statements, it was explained in whichsteps the changeover is to be expediently carried out, but nothing wassaid about how the changeover is to be advantageusly carried out in thequickest and simplest manner since in the inventive solution it is,above all, a question of keeping the times required for the individualoperations according to the inventive method as short as possible. Forthis reason, it is particularly advantageous within the scope of theinventive solution to use for the changeover a workpiece gripper whichis rotatable through 180 degrees about a (*) transversely to a spindleaxis and which operates very quickly and efficiently during changeoverof the clamping of the half-finished workpiece.

Hence, for example, in a variant of the inventive method using theabove-mentioned workpiece gripper, the changeover of the half-finishedworkpiece in the selected spindle position is carried out in the workingarea in such a way that the half-finished workpiece is removed from thespindle by means of the workpiece gripper, the workpiece gripper isrotated through 180 degrees, and the workpiece is transferred in aworkpiece holding device displaceable in the axial direction towards thespindle and is inserted by the workpiece holding device into the spindlewhich after indexing is standing in the selected spindle position.Accordingly, in this variant of the inventive method, the changeover iscarried out in such a way that the half-finished workpiece is gripped onthe machined side by the workpiece gripper and is transferred to theworkpiece holding device in such a way that the latter grips it on theside which is not yet machined and it is inserted by the workpieceholding device into the spindle after indexing of the spindle drum, inwhich case the workpiece is clamped on the machined side and so the sidewhich was not machined first is now free to be machined. This changeovermethod carried out in the working area is extremely time-saving, inparticular, when the workpiece holding device is aligned coaxially withthe spindle so when the workpiece is transferred from the spindle to theworkpiece holding device, only motions in the coaxial direction of thespindle are necessary in addition to the rotation about the axistransversely to the spindle axis.

As an alternative to the above-described variant, a further variant ofthe inventive method makes provision for the changeover of thehalf-finished workpiece in the selected spindle position to be carriedout in the working area in such a way that the half-finished workpieceis removed by means of a workpiece holding device displaceable in theaxial direction towards the spindle, transferred to the workpiecegripper which is rotated through 180 degrees and inserted by the latterinto the spindle which after indexing is standing in the selectedspindle position. This variant can be carried out just as quickly as thevariant described above and differs from it only in that thehalf-finished workpiece is removed from the spindle by the workpieceholding device. This variant is expedient particularly if bar stock isbeing machined, as will be explained in detail below.

The above-described variants are used, in particular, when thehalf-finished workpiece is gripped by the workpiece gripper axially,i.e., for example, at the front or end face.

In a further variant of the inventive method which is used, inparticular, with shaft-type parts, provision is made for the changeoverof the half-finished workpiece in the selected spindle position to becarried out in the working area in such a way that it is gripped in theradial direction, is removed from the first spindle standing in theselected spindle position, and remaining in the working area, isreversed by a 180 degree rotation of the workpiece gripper and afterremoval of the finished workpiece clamped in the second spindle in theselected spindle position due to indexing of the spindle drum, thehalf-finished workpiece is inserted into the second spindle.Accordingly, in this variant of the inventive method, transferral of thehalf-finished workpiece to an additional workpiece holding device is notnecessary since the workpiece, for example, a shaft-type part, can begripped in the radial direction, in particular, in a central regionthereof, and after rotation of the workpiece gripper through 180degrees, can be inserted with the already machined side, after indexingof the spindle drum, into the next spindle.

In this variant of the inventive method, too, the great advantage liesin the fact that the changeover of the half-finished workpiece can becarried out in such a way that it need not leave the working area and,consequently, very short changeover times can be achieved.

As a supplement to the variants of the inventive method described sofar, in which only the changeover of the half-finished workpiece wasexplained in detail, it is, furthermore, expedient, in particular, inorder to save valuable time, for a double gripper to be used asworkpiece gripper and for the finished workpiece to be removed from thespindle standing in the selected spindle position and taken away out ofthe working area. This inventive method has the additional advantagethat, in contrast with the prior art in which the finished workpiece is,for example, dropped and caught, no additional device is required forcatching the workpiece and, in addition, the finished workpiece can betransferred in a defined position to, for example, a workpiecetransporting device by means of the gripper.

In the possibilities of the inventive method described so far, it wasnot specified how the workpiece is fed to the first spindles. Withcertain parts, it is, for example, possible for the raw workpiece to befed coaxially with the first spindles, i.e., it is pushed, for example,in the form of bar stock coaxially through the spindle so there is nonecessity for either the gripper to perform additional operations or foran additional device for insertion of the workpiece to be provided inthe working area.

In the case of such coaxial feeding of the raw workpiece, in order thatit can be advanced, i.e., that the workpiece can be pushed out of thespindle to a defined extent, an additional stop must be provided for theworkpiece to be pushed thereagainst. It is, therefore, particularlysimple and time-saving if the workpiece gripper is used as delimitingstop in the coaxial feeding of the raw workpiece so the workpiecegripper need not insert this workpiece and provision of an additionalstop is unneccessary.

In all the cases in which the workpiece cannot be fed coaxially with thefirst spindles, provision is made in the inventive method, inparticular, again to save time and to achieve a method performance whichis as simple as possible, for the raw workpiece to be brought into theworking area and inserted into the first spindle standing in theselected spindle position by the double gripper.

Even in the simplest embodiment of the inventive method in whichprovision is made for the workpiece to be machined in several spindlepositions with the exception of that spindle position provided for thefeeding, removing and changing over, the advantages described at thebeginning as regards the availability of spindle positions for machiningare gained. This need not necessarily be all of the spindle positions.It is, for example, also possible for only the machining of one side tobe carried out in one spindle position with a tool combination which isnot suitable for the other side. By one spindle position being reservedfor the feeding, removing and changing over, problems regardingcontamination of all of the workpiece clamping and gripping devices bychips, which may result in damage to the workpiece, are avoided in asimple manner.

On the other hand, it is, however, necessary and also desirable in manycases for the workpiece to be machined in the spindle position providedfor the feeding, removing and changing over, which, for example, willonly be the case when the machining time for a part must be optimizedsince all of the handling operations usually take substantially lesstime than the cutting operations to be performed after each indexing ofthe spindle drum, and so the time available in the spindle positionprovided for the feeding, removing and changing over is usually notcompletely exhausted by the handling operations, which wastes valuablemachining time. Hence, for example, a last finish-turning of theworkpiece can be carried out without any difficulty in the spindleposition provided for the feeding, removing and changing over.

Machining of the workpiece in the spindle position provided for thefeeding, removing and changing over is also always necessary when theworkpiece is cut off during the changing over. This will always be thecase when bar stock is used as starting material for the workpieces andwhen, for example, on account of the required surface precision, it isnecessary for the part to be machined in one clamped state onlythroughout its entire length.

For the cutting-off operation, it is necessary for the workpiece to beheld rotatingly by the workpiece gripper or by the workpiece holdingdevice.

The workpiece can be cut off in a particularly clean and precise mannerif it is held synchronously during the cutting-off operation so the burrwhich is usually produced by the cutting-off does not occur. Also, thesynchronous holding of the workpiece during the cutting-off operationmay simultaneously constitute a first transferral of the workpiece forchangeover so the cutting-off operation is already integrated into thechangeover and hence the changeover can be carried out substantiallyquicker.

A further object of the invention is to so improve a multiple-spindleautomatic lathe of the generic kind that performance of theabove-described method is possible with it.

This object is accomplished, in accordance with the invention, with amultiple-spindle automatic lathe of the kind described at the beginningby the spindle drum being indexable in single steps, by providing asingle spindle position of the spindle drum with which the feeding meansfor raw workpieces and the conveying away means for finished workpiecesalone or in combination with the workpiece gripping device as well asthe handling unit are associated with respect to function, and by eitherraw workpieces being fed or finished workpieces being conveyed awayalternately after each indexing of the spindle drum.

This inventive multiple-spindle automatic lathe has the same advantagesas the above-described method. In addition, it should be mentioned thatthe inventive multiple-spindle automatic lathe may be of simpler designand hence also constitutes a more economically priced solution owing tothe fact that only one workpiece gripping device is required.

In the case of "simple" workpieces, in order make optimal use of thepossibilities of the inventive multiple-spindle automatic lathe, it isparticularly advantageous to provide at least a second spindle positionof the spindle drum with which both a further conveying away means forraw workpieces and a further conveying away means for finishedworkpieces alone or in combination with a further workpiece grippingdevice as well as a further handling unit are associated with respect tofunction, and in which either raw workpieces are fed or finishedworkpieces are conveyed away alternately after each indexing of thespindle drum.

The arrangement of the spindle positions can, in principle, be adaptedto the machining steps required for the respective parts. The spindlepositions are advantageously arranged opposite one another, inparticular, in such a way that they are accessible from opposite sidesof the multiple-spindle automatic lathe.

In the embodiments described so far, the design of the workpiecegripping device was not referred to in greater detail. It isadvantageous, particularly in order to achieve very short times forchangeover of the workpiece, for the workpiece gripping device tocomprise a workpiece gripper which is rotatable about an axis extendingtransversely to the spindle axis. With such a workpiece gripper, asalready explained in conjunction with the method, the half-finishedworkpiece can be changed over very efficiently and quickly.

In order to rotate this gripper through 180 degrees without having totake it out of the working area, which likewise costs valuable time, aworking area of the multiple-spindle automatic lathe is expedientlydesigned in such a way that the workpiece gripper with at least oneworkpiece gripped therein is rotatable about the axis extendingtransversely to the spindle axis.

Since it is a question of the workpiece in the tool gripper being ableto be swivelled through 180 degrees during changeover, it is expedientfor the workpiece gripper to be immobilizable in two positions orientedparallel to the spindle axis and arranged in rotated relation to eachother through a rotary angle of 180 degrees with respect to the axisextending transversely to the spindle axis, i.e., for the workpiecegripper, in the simplest case, to be exactly positionable in these twopositions and for a drive to be provided for transferring it from theone to the other position. In embodiments of the inventive solution inwhich further rotated positions of the gripper are necessary, it is,however, also conceivable for the gripper to be rotatable into anychosen angular positions and immobilizable in these.

In particular, to enable rotation of the workpiece gripper through 180degrees, in a simple manner, in accordance with the last mentionedembodiments, it is expedient for the workpiece gripping device tocomprise an arm which follows the workpiece gripper and is rotatableabout its longitudinal axis. However, this does not exhaust all of themovement possibilities of the arm within the scope of the invention. Forexample, if both grippers lie on the same side, it may be necessary forthe arm to also be displaceable in its longitudinal direction.

In the above-described inventive solution of a multiple-spindleautomatic lathe, the appearance of the workpiece gripping device was notspecified. It is, for example, expedient for the workpiece grippingdevice to comprise a double gripper in order that it can carry outchangeover of the workpiece in as short a time as possible. Severalpossibilities are conceivable for the structural design of the doublegripper. For example, the two grippers can be arranged on the same sideof an arm of the tool gripping device. On the other hand, it is,however, also possible for the two grippers to be arranged opposite eachother and coaxially with each other.

Since the workpieces usually have to be inserted into clamping means ofthe spindles or removed from these, it is necessary, in such cases, forthe workpiece gripping device to be movable parallel to axes of rotationof the spindles in order to ensure exact removal and insertion of theworkpieces.

In the embodiments of the multiple-spindle automatic lathe described sofar, the workpiece gripping device could be arranged outside of theworking area and grip into it. However, this has the great disadvantagethat the working area which should remain closed for safety reasons andalso on account of the large amounts of cooling and lubricating agentsprayed in the working area and the chips flying during the individualmachining steps, must remain open. Therefore, in a preferred version ofthe inventive multiple-spindle automatic lathe, provision is made forthe workpiece gripping device to be arranged in the working area and forboth the selected spindle position and a workpiece transporting devicearranged outside of the working area to lie within its gripping range sothe workpiece gripping device can operate with its workpiece gripper,particularly during changeover, with the working area closed, and theworking area need only be opened to grip a raw workpiece and/or deposita finished workpiece.

In order to adapt the movement possibilities of the workpiece grippingdevice to the movements to be carried out by the workpiece gripper to asgreat an extent as possible, provision is made for the workpiecegripping device to comprise a swivel axis approximately parallel to thespindles so, for example, displacement of the workpiece gripping devicein the longitudinal direction of the swivel axis automatically resultsin displacement parallel to the spindle axes.

In particular, for gripping shaft-type parts, it has proven expedientfor the workpiece gripper to be a radial gripper with which, as alreadydescribed in conjunction with the inventive method, transferral to aworkpiece holding device can then preferably be dispensed with sincerotation of the radial gripper results in reversal of the shaft-typepart without further transferral and hence after rotation of the radialgripper through 180 degrees, the shaft-type part can be inserted withthe side which has already been machined into the spindle standing inselected spindle positions.

Insofar as no shaft-type parts or similar parts to be gripped by aradial gripper are to be machined, i.e., in particular, when chuckedparts are to be machined, it has proven expedient for the workpiecegripper to be an axial gripper with which the gripping parts can then begripped from their front or end faces. So far, the workpiece holdingdevice has not been specified in greater detail. It may, for example, inorder to save space in the confined working area, be advantageous forthe workpiece holding device to be arranged outside of the working area.This has the further advantage that no problems arise as far ascontamination of the clamping means associated with the workpieceholding device is concerned.

In all cases in which the workpiece is to be changed over as quickly aspossible, it will, however, be advantageous for the workpiece holdingdevice to be arranged inside the working area since, in this case, thepaths along which the workpiece have to be moved are substantiallyshorter.

A particularly efficient arrangement of the workpiece holding device isobtained by arranging it coaxially with the associated spindle positionas it can then be moved very quickly towards the spindle or away fromthis spindle and, above all, centering motions during gripping orinsertion of a workpiece into the spindle are dispensed with.

Especially in the latter case, it is advantageous for provision to bemade for the workpiece holding device to be movable to and fro in thedirection towards the associated spindle so direct transferral of theworkpiece from the spindle to the workpiece holding device and viceversa is possible without additional use of the workpiece grippingdevice.

In quite a different embodiment of the inventive device, it may also beconceivable for the workpiece holding device to be arranged on theworkpiece gripper, thereby obtaining an extremely space-savingstructural solution in which, in addition, the workpiece holding devicemay likewise be used directly in the working area.

In all of the embodiments so far, it was not specified in which way thechange in the clamping of the workpiece from the first side to thesecond side is to be carried out. As already described within the scopeof the inventive method, multiple transferral is, for example, possible.However, since this is usually time-consuming in view of the multipleclamping or gripping operations, it likewise lies within the scope ofthe present invention for the workpiece holding device to be a workpiecereversing device so the change in the clamping of the workpiece from thefirst side to the second side can be carried out with as few transferraloperations as possible.

In particular, in an embodiment in which the workpiece is to betransferred rotatingly to the workpiece holding device or is to be cutoff, it is expedient for the workpiece holding device to comprise achuck. In particular, when the workpiece is to be cut off beforechangeover without a burr remaining, it is additionally necessary forthe workpiece holding device to be a synchronous spindle.

However, the inventive apparatus should also be suited for directlymachining bar stock so it is not necessary for raw parts of a definedlength to be made beforehand. For this reason, in an embodiment of theinventive apparatus intended for bar stock, it is desired for thefeeding means for raw workpieces to be a bar feeding device associatedwith the spindle position intended therefor. In this case--in contrastwith the machining of chucked parts--the feeding of the raw partsdirectly to the respective first spindle is carried out when it isstanding in the spindle position provided for the feeding, conveyingaway and changeover. Here, it has proven particularly expedient for theworkpiece gripper to comprise a stop surface serving as delimitation foradvance of the bar stock and to preferably include a sensor to indicatethat the bar stock is striking the stop surface.

As already explained in conjunction with the inventive multiple-spindleautomatic lathe, a great advantage of the invention consists in thefirst and second spindles comprising different clamping means forclamping the workpieces with the first or second side, respectively,and, consequently, in the clamping means being adaptable in an optimalway to the respective requirements.

On the other hand, in certain special embodiments of the inventivemultiple-spindle automatic lathe, it is, however, desirable for thefirst and second spindles to comprise clamping means which permitclamping of the workpieces on both sides since such multiple-spindleautomatic lathes can be used in a more universal way provided that noproblems are created by clamping with the same clamping means.

The inventive multiple-spindle automatic lathes have not been specifiedin greater detail in the foregoing with respect to the possibilities ofmachining the workpieces in the individual spindle positions. It isadvantageous for at least one tool carrier to be associated with eachspindle position provided for machining the workpieces. Hence a toolcarrier is to be associated with at least each spindle position, withthe exception of the spindle position for feeding, conveying away andchanging over the workpieces. However, insofar as the spindle positionfor feeding, conveying away and changing over the workpieces is also tobe used simultaneously for machining, then in accordance with theinvention, at least one tool carrier is also to be associated with it.

In accordance with the invention, machining of the workpieces in theindividual spindle positions can be carried out even more efficiently byseveral tool carriers being associated with one or several spindlepositions so several cutting operations can take place simultaneously inthese spindle positions.

If, in accordance with the invention, in each spindle position, bothmachining of the front side and machining of the rear side are to takeplace, it is necessary for the tool carrier to be displaceable in atleast one direction towards the spindles so that depending on whetherthe front or rear side is to be machined in this spindle position, thetool carrier can be displaced accordingly.

However, the inventive multiple-spindle automatic lathe is substantiallymore flexible if several tool carriers are movable in at least one planeand optimal flexibility is achieved when several tool carriers aremovable in all three directions in space.

Since it is within the scope of the present invention for the workpiecesto be machinable on both the front and rear sides in each spindleposition, and the number of tool carriers associated with the individualspindle positions cannot be optionally selected, for space reasonsalone, the tool carriers are preferably equipped with universal tools.

Another possibility of carrying out different machining operations withone and the same tool carrier consists in equipping the tool carriers,in accordance with the invention, with combination tools, i.e., suchtools as, for example, carry different types of tools on two oppositesides which can be used independently of one another by appropriatedisplacement of the tool carrier.

Further features and advantages of the present invention are the subjectof the following description and the drawings of some embodiments. Thedrawings show:

FIG. 1: a schematic perspective view of a first embodiment of aninventive multiple-spindle automatic lathe;

FIG. 2: a sectional view along line 2--2 in FIG. 1 without tool holdingdevices and workpiece holding device;

FIG. 3: a sectional view corresponding to FIG. 2 of a second embodiment;

FIG. 4(a-b: a schematic plan view of a spindle drum for machiningchucked parts in accordance with the first embodiment with a workpieceholding device illustrated out-of-line and all workpieces indicated bytheir clamping diameter only;

FIGS. 5(a-f), 6(a-e) and 7: a schematic illustration of handlingoperations in accordance with the inventive method for machining chuckedparts;

FIG. 8(a-b): a schematic plan view corresponding to FIG. 4 of a spindledrum in accordance with the second embodiment;

FIG. 9(a-b): a schematic plan view of a spindle drum for machining barstock similar to FIG. 4;

FIGS. 10(a-c), 11(a-f) and 12: a schematic illustration corresponding toFIGS. 5, 6 and 7 in accordance with the inventive method for machiningbar stock;

FIG. 13(a-f): a comparison of special cutting operations which can becarried out in each spindle position on the basis of the inventivemethod for machining bar stock, wherein all of the simultaneouslyperformed cutting operations are schematically illustrated in eachvertical column and the left column differs from the right column by oneindexing step;

FIG. 14(a-b): a schematic plan view corresponding to FIG. 8 of a spindledrum in accordance with the second embodiment for machining bar stock;

FIG. 15: a partly broken-open side view of a variant of a doublegripper;

FIG. 16: a sectional view similar to FIG. 2 of a third embodiment.

FIG. 1 shows in detail a first embodiment of a multiple-spindleautomatic lathe designated in its entirety 10. A frame 12 thereof withtwo housing sections 14 and 16 placed thereon is visible. Housingsections 14 and 16 delimit a working area 18 of the multiple-spindleautomatic lathe 10 located between these.

A spindle drum 20, likewise held on frame 12, is substantially coveredby housing section 14. Therefore, only an end face 22 of spindle drum 20which faces working area 18 is visible. Spindle drum 20 is rotatableabout an axis of rotation 24 extending substantially horizontally. Itcarries a total of six spindles S₁ to S₆, arranged in spindle drum 20 insuch a way that all spindle axes 26 of spindles S₁ to S₆ lie parallel tothe axis of rotation 24 of the spindle drum, are spaced at the samedistance from it and are also arranged at the same angular spacing fromone another relative to the axis of rotation 24.

As apparent, in particular, also from FIG. 2, spindles S₁ to S₆ can bebrought into a total of six spindle positions I to VI by the spindledrum 20 which is indexable in a stepwise manner through an anglecorresponding to the angular spacing between two successive spindles.The spindle positions are defined in a fixed manner on the housing anddo not move with rotation of spindle drum 20. In the indexed position ofspindle drum 20 illustrated in FIG. 2, spindle S₁ is associated withspindle position I, spindle S₂ with position II, etc. Spindle drum 20can be indexed one step in accordance with an indexing direction whichextends counterclockwise and is indicated by an arrow 28. Therefore,with the next indexing step, spindle S₁ will be associated with spindleposition II, spindle S₂ with spindle position III, etc.

Each of the spindles S₁ to S₆ has one clamping means which in accordancewith the illustration in FIG. 2, is a chuck 30.

This chuck 30 must be capable of clamping a workpiece W illustrated, forexample, in FIG. 5, on a first side W₁ or a second side W₂. Workpieces Ware arranged in spindles S₁ to S₆ in such a way that successive spindlesclamp workpieces W alternately on their first side W₁ or their secondside W₂. For example, in accordance with the illustration in FIG. 2,spindle S₁ is to clamp workpiece W on the first side W₁, spindle S₂workpiece W on the second side W₂, etc. Therefore, in spindles S₁, S₃and S₅, workpieces W are clamped on their first side W₁ and in spindlesS₂, S₄, S₆, workpieces W are clamped on their second side W₂.

Associated with spindle position VI is a first workpiece gripping device34 comprising an arm 40 which is mounted at the side of spindle drum 20on a front side 36 of housing section 14 facing working area 18 forrotation about a swivel axis 38 generally parallel to spindle axis 26.Arm 40 extends in a plane extending substantially perpendicularly to thespindle axis and has at its outer end a double gripper 42 comprised oftwo opposed workpiece grippers G₁ and G₂. The length of arm 40 ofworkpiece gripping device 34 is so selected that when gripping device 34has been swivelled into spindle position VI (FIG. 2), workpiece grippersG₁ and G₂ stand coaxially with the spindle standing in this spindleposition VI, in FIG. 2 spindle S₆, and hence are capable of grippingworkpieces W clamped in spindle S₆. To remove workpieces W in thisposition from spindle S₆ or to also insert them into it, arm 40 ofworkpiece gripping device 34 is mounted for displacement in thedirection of its swivel axis 38.

By swivelling of arm 40 about swivel axis 38, workpiece gripping device34 can be swivelled into a position associated with a workpiecetransporting device 44 (illustrated by dot-and-dash lines in FIG. 2), inwhich case double gripper 42 moves along a swivel circle 46. Theworkpiece transporting device 44 lies outside of working area 18 andextends along a front side 48 of housing section 14.

The workpiece transporting device 44 comprises a carrier 50 and aconveyor belt 54 which is held by guides 52 and has recesses 56 adaptedto workpiece W. Workpiece W is held in a generally horizontal positionin recesses 56. Hence an axis 58 of the workpiece W held in recess 56stands generally in the vertical direction.

In order that double gripper 42 has access to both workpieces W intransporting device 44 whose axes 58 stand generally in the verticaldirection, and to workpieces W in spindle position VI whose axes extendparallel to spindle axis 26 and hence essentially horizontally, doublegripper 42 must be rotatable about a longitudinal axis 60 of arm 40 ofworkpiece gripping device 34 extending transversely to spindle axis 26.

Workpiece transporting device 44 is controlled in such a way that, ineach case, a recess 56 stands such that the axis 58 of a workpiece Waccommodated or to be accommodated therein stands coaxially with one ofgrippers G₁ or G₂ of double gripper 42 in its position associated withworkpiece transporting device 44, thereby to enable workpiece W to beinserted into or removed from recess 56.

To machine workpieces W held in spindles S₁ to S₆ in spindle positions Ito VI, tool carriages 62 carrying tool holders 64 with tools 66 areassociated with each of these spindle positions I to VI. Depending onthe spindle position I to VI with which they are associated, the toolcarriages are designated, in addition, by the number I to VIcorresponding to the respective spindle position and by an a or b.Hence, for example, tool carriage 62, designated I_(a), is associatedwith spindle position I, and two tool carriages 62, additionallydesignated III_(a) and III_(b) are associated with spindle position III.These tool carriages are usually movable in at least one plane fixed bytwo directions standing perpendicularly on one another. It is alsoworthy of mention that there is also associated with spindle position VIto which workpiece gripping device 34 has access, a tool carriage 62,additionally designated by VI_(a). Hence machining of the workpieces Wclamped in spindles S₁ to S₆ can be carried out in each of the spindlepositions I to VI by the tools 66 carried by the respective toolcarriages 62.

In addition, as is apparent, in particular, from FIG. 1, further toolholding devices 68 are associated with each of the spindle positions Ito V. These are each displaceable parallel to the respective spindleaxis 26 in the direction towards the tools clamped in the respectivespindles S₁ to S₅. These tool holding devices 68 likewise carry tools70. The tool holding devices 68 are preferably used with their tools 70for making bores or cutting annular grooves and the like, whereas tools66 mainly serve to machine side surfaces of the workpieces W. In thesimplest case, the tool holding device 68 lies coaxially with therespective spindle axis 26 and carries a drill as tool 70.

As will be explained in detail below, it is particularly advantageousfor tools 66 and also tools 70 to be at least partly combination toolswith two cutting edges which can be used independently of one another.In this way, for example, tool 70 may have a cutting insert for drillingbores and opposite thereto a cutting insert for thread cutting. Ofcourse, in this case, the tool holding device 68 must be movable notonly parallel to the spindle axis associated with it, but alsoperpendicularly thereto in order that only one of the cutting inserts isused in each case. The same also applies to tool carriages 62 which inthe case of combination tools must be displaceable not only exclusivelyin the radial direction 72 relative to the respective spindle axis 26,but must, in addition, be movable in at least one directionperpendicularly to this radial direction 72. This direction extends, forexample, parallel to the respective spindle axis 26. It is, however,also possible for this additional direction to lie parallel to the frontside 36 of housing section 14.

In the first embodiment of the inventive apparatus, it is not a toolholding device 68 that is associated with spindle position VI butinstead of that a workpiece holding device in the form of a push-indevice 74 which is arranged coaxially with the spindle axis 26 of thespindle standing in this spindle position VI and is also displaceable inthis direction. At its end associated with the respective spindle, thepush-in device 74 carries a clamping means 76 which may, for example, bea collet or a chuck. The push-in device 74 is movable in the directionof the spindle standing in spindle position VI to such an extent that itcan grip the workpiece W clamped in this spindle on the still free sideW₁ or W₂.

In a second embodiment of the inventive multiple-spindle automatic lathe10, a second workpiece gripping device 34', identical with workpiecegripping device 34, is provided in mirror-image relation to a verticalmirror plane 25 extending through the axis of rotation 24 of spindledrum 20. Hence all parts of workpiece gripping device 34' have the samereference numerals as those of workpiece gripping device 34 and areadditionally designated by an '. For a description of these, referenceis made to the description of workpiece gripping device 34.

In a similar manner, a workpiece transporting device 44' having the sameparts as workpiece transporting device 44 is associated with workpiecegripping device 34'. Hence all reference numerals for identical partsare the same but are designated by an additional ' in the case ofworkpiece transporting device 44'.

In addition, a workpiece holding device which can perform the sameoperations as push-in device 74 is associated as push-in device 74' withspindle position III.

The function of the first embodiment of the inventive multiple-spindleautomatic lathe will be explained by the example of workpieces Wrepresenting chucked parts with reference to FIGS. 4 to 7, assuming thatthe chucks 30 of spindles S₁ to S₆ are suited for clamping workpieces Wrepresenting chucked parts both on their first side W₁ and on theirsecond side W₂. More particularly, spindles S₁, S₃ and S₅ are providedfor clamping workpieces W on their first sides W₁ and spindles S₂, S₄and S₆ for clamping workpieces W on their second sides W₂.

A schematic illustration of the performance of the inventive method withthe described first embodiment of the multiple-spindle automatic latheis given in FIGS. 4a and 4b. In these Figures, workpiece W itself is notillustrated, but merely indicated by its clamping diameter indot-and-dash lines. FIGS. 4a and 4b differ in that spindle drum 20 inFIG. 4b is indexed one step further than in FIG. 4a. Hence in FIG. 4b,spindle S₆ is standing in spindle position VI, whereas in FIG. 4a,spindle S₁ is standing in spindle position VI.

When, as shown in FIG. 4a, spindle S₁ provided for clamping chuckedparts W on their first sides W₁ arrives in spindle position VI, thefollowing method steps are carried out:

First, the chucked part W clamped on its first side W₁ in spindle S₁,which has already gone through a machining cycle through spindlepositions I to VI and hence is a half-finished part W_(h), is removed bygripper G₂, not illustrated in the drawings, and transferred to push-indevice 74, drawn out-of-line towards the left in FIG. 4, for reasons ofclarity, which likewise grips this half-finished part W_(h) on its firstside W₁. A raw workpiece or part W_(r) delivered by workpiecetransporting device 44 is then inserted into the now "empty" spindle S₁by gripper G₁ and clamped in this spindle ₁.

Spindle drum 20 is next indexed one step, as shown in FIG. 4b.

The raw part W_(r) clamped in spindle S₁ is standing in spindle positionI and is machined there in accordance with a given program.

Spindle S₆ carrying a workpiece W clamped on the second side W₂ has nowarrived in spindle position VI. This workpiece W clamped on side W₂ hasalready passed through spindle positions I to VI twice, a first time formachining the second side W₂ up to the half-finished part W_(h) and asecond time for machining the first side W₁ up to a finished part W_(f).This finished part W_(f) is removed from spindle S₁ by gripper G₁ andtransferred to workpiece transporting device 44. The half-finished partW_(h) clamped on its first side W₁ is then transferred to the now"empty" spindle S₆ by push-in device 74 and it can, therefore, beclamped on its second side W₂ by spindle S₆. Spindle drum 20 is thenindexed one step further and so spindle S₅ now stands in spindleposition VI. The half-finished part W_(h) clamped in spindle S₆ nowpasses through all of the spindle positions I to V and arrives inspindle position VI again as finished part W_(f) which can then beremoved.

When spindle S₅ is standing in spindle position VI, the situation is thesame as in FIG. 4a, i.e., the same method steps are carried out again,as already described in FIG. 4a, with the only difference that it is nolonger S₁ that is standing in spindle position VI but spindle S₅.

The inventive method, illustrated in FIGS. 4a and 4b, can be summarizedin the following way:

First, a raw part W_(r) is clamped on its first side W_(r1) in one ofspindles S₁, S₃ and S₅ in spindle position VI. In this clamped state, itpasses through spindle positions I to V and arrives in spindle positionVI after machining of its second side W_(r2) as half-finished partW_(h). There, the half-finished part W_(h) is removed, changed over intopush-in device 74, awaits the next indexing step there and can then beinserted by push-in device 74 into one of spindles S₂, S₄ and S₆ in sucha way that the half-finished part W_(h) is clamped on its second sideW_(h2). Hence machining of the first side W_(h1) is now possible as itpasses through spindle positions I to V, and so this half-finished partW_(h) then arrives in spindle position VI as finished part W_(f) and canbe removed.

The steps to be carried out in spindle position VI for feeding a rawpart W_(r), changing over a half-finished part W_(h) and removing afinished part W_(f) will now be explained in detail with reference toFIGS. 5 to 7.

First, a workpiece W_(r) is delivered as raw part by workpiecetransporting device 44 and oriented in recess 56 in such a way that itcan be gripped on its second side W_(r2) by workpiece gripper G₁ whenworkpiece gripping device 34 is in the position (illustrated bydot-and-dash lines in FIG. 2) associated with workpiece transportingdevice 44. Workpiece gripping device 34 is now swivelled about swivelaxis 38 into the position associated with spindle position VI, anddouble gripper 42 is simultaneously rotated about longitudinal axis 60of arm 40 to such an extent that double gripper 42 stands coaxially withspindle S₁ standing in spindle position VI with gripper G₂ facingspindle S₁. Hence gripper G₁ with the workpiece W_(r) gripped on sideW_(r2) faces away from spindle S₁. In this position, double gripper 42stands between spindle S₁ in spindle position VI and the push-in device74 (FIG. 5a) associated with this spindle position.

It was already mentioned that spindles S₁, S₃ and S₅ are provided forclamping workpieces W on their first side W₁. For this reason, spindleS₁, as shown in FIG. 5a, is already carrying a half-finished workpieceW_(h) which is clamped on the first side W₁ and has gone through onemachining cycle. This means that the workpiece W_(h) clamped spindle S₁was inserted in spindle position VI into spindle S₁ six indexing stepsof spindle drum 20 previously and was machined to a half-finished partby tools 66 and 70 as it passed through spindle positions I to V. Hence,as shown in FIG. 5a, it has a stepped bore 80 and has also alreadyundergone preliminary machining on a circumferential surface 82.

As indicated by arrow 100, workpiece gripping device 34 is now moved inthe direction of swivel axis 38 towards spindle S₁ and so gripper G₂ cangrip workpiece W_(h) clamped in spindle S₁ on the second side W_(h2)(FIG. 5b). In order to be able to grip workpiece W_(h) clamped inspindle S₁ with gripper G₂, the chuck 30 of spindle S₁ is opened.Workpiece gripping device 34 can then be moved away again in thedirection of swivel axis 38 from spindle S₁ in the direction of arrow102 and so double gripper 42 again stands between spindle S₁ and push-indevice 74 (FIG. 5c). Subsequent rotation of double gripper 42 through180 degrees in accordance with an arrow 104 results in gripper G₁ nowfacing spindle S₁ with its raw part W_(r) (FIG. 5d).

Insertion of raw part W_(r) into spindle S₁ is carried out by renewedmotion of workpiece gripping device 34 parallel to swivel axis 38 in thedirection of arrow 106 towards spindle S₁. Hence workpiece W_(r) isinserted with its first side W_(r1) into chuck 30 of spindle S₁ and canthen be clamped (FIG. 5e). After gripper G₁ is opened, workpiecegripping device 34 is again moved in the direction of arrow 108 awayfrom spindle S₁ into the position located between it and push-in device74. Raw part W_(r) is thus clamped in spindle S₁ and can subsequently gothrough a machining cycle through all of the spindle stations I to V(FIG. 5f).

For this reason, spindle drum 20 is indexed one step and so spindle S₆now stands in spindle position VI, as shown in FIG. 6a. The spindle S₁shown in dashed lines in FIG. 6a with raw part W_(r) is now standing inspindle position I and is machined there by, for example, tool 66.

Before or during indexing of spindle drum 20, workpiece gripping device34 is moved parallel to swivel axis 28 in the direction of push-indevice 74 and so the half-finished part W_(h) held in gripper G₂ can begripped by clamping means 76 of push-in device 74.

As explained at the beginning, spindles S₂, S₄ and S₆ are provided forclamping workpieces W on their second sides W₂. The spindle S₆ shown inFIG. 6a carries a workpiece W_(f) representing a finished part when itis standing in spindle position VI. This was inserted as half-finishedpart W_(h) into spindle S₆ in spindle position VI--as will be explainedin detail below--and has gone through a machining cycle covering spindlepositions I to V. Workpiece W_(f) was, for example, provided with afurther stepped bore 84 and, in addition, machined on a circumferentialsurface 86 associated with the first side W_(f1). Hence workpiece W_(f)is now available as finished part in spindle position VI.

After gripper G₂ is opened, workpiece gripping device 34 is movedparallel to swivel axis 38 in the direction of arrow 112 towards spindleS₆ and so gripper G₁ can grip finished part W_(f) on the first sideW_(f1) (FIG. 6b).

The chuck 30 of spindle S₆ is opened to enable workpiece gripping device34 to be moved in the direction of arrow 114 into that position again inwhich double gripper 42 is located between spindle S₆ and push-in device74 (FIG. 6c). In order to deposit finished part W_(f), the entireworkpiece gripping device with the double gripper is swivelled alongswivel circle 46 into the position associated with workpiecetransporting device 44 and simultaneously rotated about longitudinalaxis 60 through 90 degrees, thereby to enable finished part W_(f) to bedeposited in recess 56 of conveyor belt 54 from which workpiece W_(r)was previously removed as raw part.

Since double gripper 42 is no longer standing between push-in device 74and spindle S₆, push-in device 74 can be moved in the direction of arrow116 out of its position shown in FIG. 6c in the direction of spindle S₆and the half-finished part W_(h) transferred to spindle S₆ (FIG. 6d).After transferral, push-in device 74 is driven back again in thedirection of arrow 118 away from spindle S₆ into its original position(FIG. 6e). Half-finished part W_(h) is now clamped on a second sideW_(h2) in spindle S₆ and can subsequently be made to undergo a machiningcycle in spindle positions I to V by indexing the spindle drum.

After spindle drum 20 is indexed again one step, spindle S₅ carrying ahalf-finished part W_(h) clamped on its first side W_(h1) (FIG. 7),therefore, appears in spindle position VI. Hence the initial situationis the same as that in FIG. 5a and the same steps are to be carried outas in FIGS. 5 and 6. Of course, workpiece gripping device 34 must beable to remove a raw part W_(r) from workpiece transporting device 44beforehand. To this end, after insertion of the finished workpieceW_(f), the workpiece transporting device is to be moved further so thata raw part W_(r) is again available for gripper G₁ in a following recess56. After all transfers, as described above for spindle S₁ in spindleposition VI, have been carried out with spindle S₅ standing in spindleposition VI, spindle drum 20 is indexed again one step. Hence spindle S₄now appears in spindle position VI and the situation is the same as inFIG. 6a and, consequently, also the transfers illustrated in FIGS. 6 ato 6e are to be carried out.

In FIGS. 8a and 8b, performance of the inventive method is schematicallyillustrated with a multiple-spindle automatic lathe according to thesecond embodiment illustrated in FIG. 3.

FIGS. 8a and 8b likewise differ in that spindle drum 20 is indexed onestep further in FIG. 8b than in FIG. 8a and, consequently, spindle S₆ isstanding in spindle position VI in FIG. 8b, whereas spindle S₁ isstanding in spindle position VI in FIG. 8a.

In contrast with the first embodiment, illustrated in FIGS. 4a and 4b,in the second embodiment both workpieces W, fed as raw parts W_(r) andconveyed away as finished parts W_(f), in spindle position VI, andworkpieces V, fed as raw parts V_(r) and conveyed away as finished partsV_(f), in spindle position III, are simultaneously machined.

When, as shown in FIG. 8a, spindle S₁ has arrived in spindle positionVI, a workpiece V clamped on its first side V₁ and, therefore, alreadymachined to a half-finished part V_(h) on the second side is removedthere and fed to the push-in device 74, drawn out-of-line towards theleft, for reasons of clarity, by which it is likewise held on its firstside W₁. This half-finished part V_(h) arriving in spindle position VIwas originally inserted in spindle position III (see FIG. 8b) as rawpart V_(r), clamped on its first side and, therefore, machined on itssecond side in spindle positions IV and V.

A raw part W_(r) of workpiece W is now inserted from the outside intothis now "empty" spindle S and likewise clamped on its first side W₁.This raw part W_(r) is now machined on its second side as it passesthrough spindle positions I and II and arrives in spindle position IIIas half-finished part W_(h) (see FIG. 8b). There, this half-finishedpart W_(h) is removed from the spindle and inserted into push-in device74', and, in turn, a raw part V is simultaneously fed to the now emptyspindle.

In FIG. 8b, spindle drum 20 is indexed one step, i.e., spindle S₆ is nowstanding in spindle position VI. A finished part W_(f), clamped on itssecond side W₂, now arrives in it and is conveyed away there. Thisfinished part W_(f) was previously removed as half-finished part (seeFIG. 8a) from push-in device 74' in spindle position III and insertedinto the spindle in which it was clamped on its second side W₂. Hencethe half-finished part W_(h) was able to be machined on its second sideW_(h2) as it passed through spindle positions IV and V until it arrivedas finished part W_(f) in spindle position VI.

The half-finished part V_(h) fed to push-in device 74 during theprevious indexing step is now inserted into the empty spindle S₆ andclamped on its second side V_(h2). It can now pass through spindlepositions I and II in which it is machined on its first side W_(h1)until it arrives as finished part V_(f) in spindle position III (seeFIG. 8a). In it, the finished part V_(f) is removed and conveyed away,and, simultaneously, as explained above, a half-finished part W_(h) isinserted into the now "empty" spindle and clamped on its second sideW_(h2).

Accordingly, in the inventive method using the second embodiment of themultiple-spindle automatic lathe, a raw part W_(r) is clamped on itsfirst side by one of spindles S₁, S₃ and S₅ in spindle position VI,passes through spindle positions I and II with this spindle, arrives inspindle position III as half-finished part W_(h), is removed there andinserted into push-in device 74' as half-finished part W_(h). In thispush-in device 74', the half-finished part W_(h) awaits an indexing stepof spindle drum 20, and so one of spindles S₂, S₄, S₆ then stands inspindle position III. If this is the case, the half-finished part W_(h)is then removed from push-in device 74' and inserted into one ofspindles S₂, S₄, S₆ which can clamp the half-finished part W_(h) on itssecond side W_(h2). In this clamped state, the half-finished part W_(h)passes through spindle positions IV and V in which this half-finishedpart W_(h) is machined on the first side. When the half-finished partW_(h) has then arrived in spindle position VI as finished part W_(f), itcan be removed there and conveyed away. The procedure with workpieces Vis carried out in a similar manner, but based on spindle position III. Araw part V_(r) is inserted in spindle position III into one of spindlesS₁, S₃ and S₅, and clamped there on its first side V_(r1). In thisclamped state, it passes through spindle positions IV and V, is machinedthere on its second side V_(r2) and arrives as half-finished part V_(h)in spindle position VI (see FIG. 8a). There, the half-finished partV_(h) is removed and inserted into push-in device 74. After a furtherindexing step, the half-finished part V_(h) is removed again frompush-in device 74 and inserted into one of spindles S₂, S₄, S₆ andclamped in it on its second side V_(h2). The machining of the first sideV_(h1) can then be carried out in spindle positions I and II until thehalf-finished part V_(h) on which machining has now been completedarrives again in spindle position III as finished part V_(f) and can beconveyed away there.

The individual changeover steps carried out in spindle positions VI andIII correspond to those of FIGS. 5 to 7, with the only difference thatthe half-finished part W_(h), V_(h) changed over in these spindlepositions VI and III is not fed in these spindle positions but in therespective other spindle position. Reference is, therefore, also made tothe corresponding parts of the description of FIGS. 5 to 7.

As is apparent from the above description, workpieces W and V may bebasically different workpieces, but they must have such similarity withone another that spindles S₁, S₃ and S₅ and also spindles S₂, S₄ and S₆enable, without conversion, workpieces W and V to be clamped on theirfirst and second sides, respectively. On the other hand, it is likewisewithin the scope of the inventive solution to work with identicalworkpieces W and V, thereby enabling the efficiency of the inventivemultiple-spindle automatic lathe to be doubled because a total of fourmachining stations is adequate, in each case, for these workpieces W andV.

Provision may also be made for machining bar stock with the firstembodiment of the inventive multiple-spindle automatic lathe.Accordingly, in such a case, workpieces W are not fed as unmachinedchucked parts, but rather in the form of bar stock. For this reason,spindles S₁, S₃ and S₅ are not provided with a chuck 30, in each case,but with a collet 32, in each case, and bar stock 120 is fed throughcoaxially with the collets 32 of spindles S₁, S₃ and S₅. Also, theworkpiece holding device is not a push-in device, but rather asynchronous spindle 74 which can be driven at the same speed as thespindle standing in spindle position VI and, in addition, is movableexactly like the push-in device in the direction of the spindle standingin spindle position VI.

FIGS. 9a and 9b illustrate schematically performance of the inventivemethod for machining bar stock on a multiple-spindle automatic latheaccording to the first embodiment shown in FIGS. 1 and 2. Herein,workpiece W' itself is not illustrated, but, in each case, its clampingdiameter is indicated by dot-and-dash lines only.

As is to be seen in FIG. 9a, a half-finished workpiece W_(h') in spindleS₁ arrives in spindle position VI. However, this half-finished part isstill connected to the bar stock pushed coaxially through spindle S₁ orits collet 32, respectively. For this reason, simple changeover of thehalf-finished part W_(h') is not possible in spindle position VI, butrather the synchronous spindle arranged coaxially with the collet isbrought up to the half-finished part, grips it and the half finishedpart W_(h') is cut off from the bar stock 120 jointly with thesynchronous spindle 74. Hence the half-finished part W_(h') has thenbeen transferred to the synchronous spindle 74 and so a new raw partW_(r') can be made available for machining in spindle positions I to Vafter the bar stock has been advanced.

After spindle drum 20 has been indexed one step, spindle S₆ arrives inspindle position VI. This situation is illustrated in FIG. 9b. In thisposition, spindle S6 holds a finished part W_(f') ready and it isconveyed away. The half-finished part W_(h') temporarily stored insynchronous spindle 74 is now inserted into the "empty" spindle S₆ insuch a way that it can be clamped with its second side W_(h2') inspindle S₆. Spindle S₆ can then pass through spindle stations I to V andthe half-finished part W_(h') then arrives again in spindle position VIas finished part W_(f') and can, therefore, be removed.

In summary, a raw part W_(r') is made available in spindles S₁, S₃ andS₅ in spindle position VI by advancing the bar stock 120 and afterpassing through spindle positions I to V it arrives again in spindleposition VI, is removed from it as half-finished part W_(h') by beingcut off by synchronous spindle 74, is temporarily stored in synchronousspindle 74 and then inserted again as half-finished part W_(h') into oneof spindles S₂, S₄ and S₆ and, clamped with its second side W_(h'2),passes through spindle positions I to V so as to arrive again asfinished part W_(f') in spindle position VI.

The individual method steps to be carried out in spindle position VIwill now be explained in detail in the following FIGS. 10 to 12.

Once spindle S₁ appears in spindle position VI, it carries a workpieceW_(h) which owing to the previous machining cycle in spindle positions Ito V was provided, for example, with grooves 122 and bores 124 andrepresents a half-finished part which is, however, still connected tothe bar stock 120 and on account of the collets 32 clamping the barstock 120 is likewise still clamped in spindle S₁ (FIG. 10a). To cut offthe half-finished workpiece W'_(h), the synchronous spindle 74 arrangedin its initial position in spaced relation to spindle S₁ is moved in thedirection of an arrow 126 towards spindle S₁, to enable its chuck 76 toclamp workpiece W'_(h) on the second side W'_(h2) (FIG. 10b). After bothspindle S₁ and synchronous spindle 74 have been made to rotate, thecutting-off of workpiece W'_(h) can be carried out by means of the toolcarriage VIa associated with spindle position VI and the tool 66 carriedby it. After the cutting-off, workpiece W'_(h) remains clamped in chuck76 of synchronous spindle 74. Synchronous spindle 74 is then moved backin the direction of an arrow 128 into its initial position away fromspindle S₁, and the bar stock 120 in spindle S₁ can be advanced duringtemporary release of collet 32 in the direction of synchronous spindle74 to such an extent that this workpiece W'_(r) representing a raw partis clamped in spindle S₁ and is available for the subsequent machiningcycle in spindle positions I to V. Therefore, after six indexing stepsof spindle drum 20, a half-finished workpiece W'_(h) with grooves 122and bores 124 arrives in spindle position VI.

Since a path of advance of the bar must be precisely fixed and measuredfor advance of the bar stock 120, it is advantageous for gripper G₁ tobe driven in the path of advance of the bar to an appropriate distancein front of spindle S₁ and hence serve as delimiting stop for advance ofthe bar.

After indexing of spindle drum 20, spindle S₁ stands in spindle positionI and spindle S₆ now in spindle position VI (FIG. 11a), and synchronousspindle 74 is still holding workpiece W'_(h) representing ahalf-finished part clamped in its chuck 76. The spindle S₁ with theworkpiece representing a raw part standing in spindle position I is nowillustrated in dashed lines in FIG. 11a.

In this position, the workpiece gripping device 34 is swivelled into itsposition associated with spindle position VI and so double gripper 42stands coaxially with spindle axis 26 and hence also with synchronousspindle 74.

Spindle S₆ carries a workpiece W'_(f) clamped on the second side W'₂which in the previous machining cycle in spindle positions I to V hasbeen provided with additional grooves 126 and bores 128 and nowrepresents the finished part. Transfer of the workpiece W'_(f)representing a finished part and still clamped in spindle S₆ toworkpiece gripper G₁ of double gripper 42 and also of the workpieceW'_(h) representing a half-finished part and still clamped insynchronous spindle 74 to gripper G₂ is carried out during simultaneousdisplacement of workpiece gripping device 34 in the direction of itsswivel axis 38 towards spindle S₆ and displacement of synchronousspindle 74 in the same direction so that gripper G₁ gets to grip thefinished part W'_(f) on the first side W'_(f1) and gripper G₂ thehalf-finished part W'_(h) likewise on the first side W'_(h1) (FIG. 11b).

After grippers G₁ and G₂ are closed and chuck 30 of spindle S₆ and alsochuck 76 of synchronous spindle 74 are opened, synchronous spindle 74and workpiece gripping device 34 are moved away from spindle S₆ in thedirection of an arrow 132 and so--as shown in FIG. 7c--synchronousspindle 74 is standing in its initial position and double gripper 42between spindle S₆ and synchronous spindle 74.

After double gripper 42 is rotated about longitudinal axis 60 of arm 40through 180 degrees, gripper G₂ faces spindle S₆ with the half-finishedpart W'_(h) (FIG. 11d). Therefore, the half-finished part can beinserted into the free chuck 30 of spindle S₆ and clamped there (FIG.11e) by displacement of double gripper 42 in the direction of arrow 134.After gripper G₂ is opened, workpiece gripping device 34 is again movedaway from spindle S₆ in the direction of an arrow 136 to such an extentthat double gripper 42 stands between spindle S₆ and synchronous spindle74 (FIG. 11f).

Hence the half-finished part W'_(h) is clamped in spindle S₆ and can nowundergo a further machining cycle in spindle positions I to V and havinggone through this machining cycle arrives in spindle position VI asfinished part W'_(f).

Now only the finished part W'_(f) is held in gripper G₁ and can bedeposited in one of the recesses 56 of workpiece transporting device 44by workpiece gripping device 34 being swivelled about swivel axis 38into the position associated with workpiece transporting device 44.Accordingly, in the case of the second embodiment, workpiecetransporting device 44 merely serves to convey finished parts away andnot to additionally feed raw parts.

Next, spindle drum 20 is indexed one step and so spindle S₅ then appearsin spindle position VI (FIG. 12). Like spindle S₁, it carries ahalf-finished part produced in a previous machining cycle. The procedurecarried out with it is then the same as with the half-finished part inspindle S₁, i.e., a cutting-off operation is carried out with the aid ofsynchronous spindle 74 and so the half-finished part W'_(h) is thenclamped on its second side W'_(h2) in chuck 76 of synchronous spindle74. Spindle S₆ now standing in spindle position I is illustratedsupplementarily in dot-and-dash lines in FIG. 12 and, in like manner,double gripper 42 which in this position transfers the finished part toworkpiece transporting device 44.

With reference to the above-described first and second embodiments ofthe inventive multiple-spindle automatic lathe, the feeding of rawworkpieces W_(r), the conveying away of finished workpieces W_(f) andthe changing over of half-finished workpieces W_(h) from the spindlesS₁, S₃, S₅, also referred to as first spindles, to the spindles S₂, S₄,S₆, also referred to as second spindles, with the clamping of theworkpiece being simultaneously changed from the first side W₁ to thesecond side W₂, have been explained by way of example for both chuckedparts and bar-type parts. However, no explanations were given about themachining operations in spindle positions I to V.

Since all of the spindle positions I to V are passed through by both theraw parts held in the first spindles during a machining cycle from theraw part to the half-finished part, and the half-finished parts held bythe second spindles during the machining cycle from the half-finishedpart to the finished part, in accordance with the invention, spindlepositions I to V are equipped with tools 66 and/or 70 in such a waythat, as far as possible, machining of the workpieces can be carried outin each of the spindle positions I to V. This is easily possible withconsistent use of the numerical control system of the multiple-spindleautomatic lathes as both the tool carriages 62 and the tool holdingdevices 68 can be controlled in accordance with the part to be machined,depending on whether a first spindle or a second spindle is standing inthe respective spindle position. Hence, for example, universal tools canbe used in the machining of the raw part to the half-finished part fordifferent cutting operations than in the machining of the half-finishedpart to the finished part.

As mentioned above, combination tools with two cutting edges can also beused. Hence one cutting edge can be utilized in the machining cycle fromthe raw part to the half-finished part and the other cutting edge in themachining cycle from the half-finished part to the finished part.

Of course, several tools may also be used simultaneously in each spindleposition. For example, both tools 66 of tool carriages IIIa, IVa and Vaand those of tool carriages IIIb, IVb and Vb may be used simultaneouslyin spindle positions III, IV and V in accordance with FIG. 2. It is alsoconceivable for tools 70 of the tool holding devices 68 associated withthese spindle positions to likewise be used in addition.

This variety of uses of the tools in each of the spindle positions I toV facilitates, above all, in complicated cutting operations, themachining of workpieces W and hence results in extremely short machiningtimes.

Finally, it should be mentioned that the tool carriage VIa associatedwith spindle position VI may, in addition to cutting off bar-type parts,also be used for additional machining operations on chucked parts orbar-type parts, for example, for a last finish-turning of the parts,since there is usually sufficient time between the respective indexingsteps, the time between the individual indexing steps being limited bythe longest machining time in one of spindle positions I to V. Hencethose for the individual transfer steps of the parts between thespindles in spindle position VI and the gripper and between thesynchronous spindle and the push-in device are of no significance.

With reference to the first embodiment of the inventive multiple-spindleautomatic lathe, special operations in the machining of bar stock in theindividual spindle positions I to VI are specified as examples for manymachining operations, in order to explain again in detail the differentor partly also identical machining of workpieces clamped in the firstspindles S₁, S₃, S₅ or in the second spindles S₂, S₄, S₆. To this end,all workpieces occurring at the same point in time for machining inspindle positions I to VI are illustrated below one another in FIGS. 13ato 13f. In the left-hand vertical row, a first spindle is standing inspindle position I and, consequently, in spindle position II a secondspindle, etc., whereas in the right-hand vertical row, a second spindleis standing in spindle position I and in spindle position II a firstspindle. Passage of a raw part during machining up to the finished part,commencing at the top part of the left-hand column, is indicated by thethick black arrows.

As shown in FIG. 2, only tool carriage Ia with tool 66 which, in theinstant case, has a flat cutting edge for cutting an annular groove 140in a lateral area 142 of a cylindrical workpiece W representing a rawpart, is associated with spindle position I. Simultaneously associatedwith spindle position I is the tool holding device 68 with tool 70 whichcarries a drill 144 for making a bore 146 in an end face 148 of thecylindrical workpiece W'_(r) representing a raw part.

Hence in a machining of a raw part clamped in the first spindles S₁, S₃,S₅ --as shown in FIG. 13a--in spindle position I, the annular groove 114is cut and the bore 146 is made.

If, on the other hand, a workpiece which is already half-finished andclamped on the second side W'_(f2) in the second spindles S₂, S₄, S₆ isawaiting machining in spindle position I, then only drill 144 is used.It serves to make a bore 150 in an end face 152 opposite end face 148.

Simultaneously with machining of a raw part in spindle position I, themachining of a half-finished part clamped in the second spindles iscarried out in spindle position II (FIG. 13b) by the tool 66 which is astandard turning tool 153 which is held by tool carriage IIa and is usedto turn a step 154 starting from end face 152. Also associated with thisspindle position is a tool holding device 68 with a drill 156 whichmakes the bore 150 deeper from the end face 152. A workpiece W'_(r)clamped in one of the first spindles in spindle position II is machinedwith the same tools 153, 156, in which case turning tool 153 serves toturn the lateral area 142 from end face 148 to annular groove 140 anddrill 156 makes the bore 146 deeper.

In spindle position III (FIG. 13c) a widened turning tool 158 forcutting grooves is held by tool carriage IIIa and serves to widen thegroove 140 on all workpieces W clamped in the first spindles.Simultaneously mounted in the tool holding device 68 associated withthis spindle position is a turning tool 160 for internal machining, bymeans of which the bore 146 is widened. On the workpieces clamped in thesecond spindles, the turning tool 160 for internal machining is likewiseused to widen bore 150 in a front region thereof. On the other hand, theturning tool 158 for cutting grooves is not used, but rather anotherturning tool 162 for cutting grooves which is held on tool carriage IIIband serves to cut a groove 164 in step 154.

In spindle position IV (FIG. 13d) all of the workpieces W'_(h) clampedin the second spindles are provided in the region of the step 154 with athread which is made by a turning tool 166 for cutting threads which isheld on tool carriage IVa. In this spindle position, turning tool 166for cutting threads is likewise used on all workpieces W'_(h) clamped inthe first spindles, but, in addition to this, another turning tool 168for cutting threads which is held on tool carriage IVb and also aturning tool 170 for internal machining which is mounted in the toolholding device 68 associated with this spindle position are used forcutting an annular groove in bore 146.

In spindle position V (FIG. 13e) a turning tool 172 for cutting grooveswhich is held on tool carriage Va and also a turning tool 174 formultiple use held on the tool holding device 68 associated with spindleposition V are used on the workpieces W'_(r) clamped in the firstspindles. The last-mentioned turning tool 174 is also used on theworkpieces W'_(h) in the second spindles, whereas instead of the turningtool 172 for cutting grooves, a drill arranged on tool carriage Vb isused to make a bore.

Finally, in spindle position VI (FIG. 13f) half-finished parts clampedin the first spindles are merely cut off by the above-mentioned cut-offtool 178 held on tool spindle VIa. On the finished workpieces arrivingin the second spindles in spindle position VI, no further machining iscarried out in this spindle position.

The performance of the inventive method on a multiple-spindle automaticlathe according to the second embodiment shown in FIG. 3 is described inFIGS. 14a and 14b and, exactly as in FIGS. 9a and 9b, machining of barstock is carried out. To this end, in both spindle position VI andspindle position III, raw parts W_(r') and V_(r') are fed by advancingthe bar stock in the collets and finished parts W_(f') and V_(f') areconveyed away.

The method is carried out as follows for workpieces W'. In spindleposition VI, the bar stock is advanced in each of the spindles S₁, S₃and S₅ and so a raw part W is available for machining. It is then madeto pass through spindle positions I and II by indexing of spindle drum20 and arrives as half-finished part W_(h') in spindle position III.There, it is cut off with the aid of synchronous spindle 74' and remainsin this synchronous spindle 74' until the next indexing step. With thenext indexing step, one of the spindles S₂, S₄ and S₆ arrives in spindleposition III and so the half-finished part W_(h') can be inserted intoone of these spindles by synchronous spindle 74', more particularly, insuch a way that it is clamped on its second side W_(h2'). In thisclamped state, machining of the second side is possible in spindlepositions IV and V. The half-finished part W_(h') then arrives asfinished part W_(f') in spindle position VI and is removed from thespindle in it and conveyed away.

Passage of a workpiece V, starting at spindle position III, is similar.There, bar stock is similarly advanced in one of the spindles S₁, S₃ andS₅ standing in spindle position III and so a raw part V_(r') isavailable. It then passes through spindle positions IV and V and arrivesin spindle position VI as half-finished part V_(h') (FIG. 14a), is cutoff there with the aid of synchronous spindle 74 and remains in thissynchronous spindle until after indexing of spindle drum 20 (FIG. 14b).The half-finished part V_(h') is then inserted into one of spindles S₂,S₄ and S₆ in such a way that it is clamped in it with its second sideW_(h2') and can then pass through spindle positions I and II forcompletion of the machining. Hence it arrives again in spindle positionIII as finished part V_(f') (FIG. 14a), is removed there and conveyedaway.

Accordingly, performance of the inventive method with the secondembodiment of the multiple-spindle automatic lathe resembles that inFIGS. 9a and 9b, with the difference that the changeover of therespective half-finished part W_(h') and V_(h') is not carried out inspindle position VI, III in which it is fed, but rather in therespective opposite spindle position.

As mentioned above, to enable gripper 61 to be advantageously used asdelimiting stop for advance of the bar, as shown in FIG. 15, its insidejaw surfaces 210 serve as stop surfaces for the end face 212 of the barstock and, in addition, there protrudes between these a feeler 214 of asensor 216 beyond the plane formed by the inside jaw surfaces. Hencewhen the end face 212 strikes the stop surfaces 210, the sensor 216 isactuated by the feeler and reports this to a control system which can,therefore, recognize the presence of bar stock.

A third embodiment of the inventive multiple-spindle automatic lathe,illustrated in FIG. 16, differs from the first embodiment only in theway in which the double gripper 42, designated 42" in FIG. 16, isdesigned. This double gripper 42" is provided, in particular, for thepurpose of gripping in the radial direction workpieces Z in the form ofshaft-type parts approximately in a central region thereof. In thisrespect it differs from the double grippers 42 and 42' described so far,as these gripped the workpieces at the front or end face and are,therefore, to be referred to as axial grippers.

The double gripper 42" is preferably arranged relative to its swivelaxis 38 in such a way that the workpieces Z held in grippers G₁ or G₂cut the swivel circle 46 with their longitudinal axes 200, and sowithout a change in the radial spacing of double gripper 42" from swivelaxis 38, each of the workpieces Z can be aligned coaxially with thespindle axis 26 standing in spindle position VI by mere swivelling ofdouble gripper 42" about swivel axis 38.

The multiple-spindle automatic lathe according to the second embodimentoperates, in principle, in exactly the same way as the multiple-spindleautomatic lathe according to the first embodiment illustrated in FIGS. 5to 7, with the only difference that after rotation of the double gripperillustrated from FIG. 5c to FIG. 5d, the half-finished part Z_(h) isalready reversed and stands available in a position in which it can beinserted into the spindle which after indexing is standing in spindleposition VI. Hence insertion of the half-finished part into this secondspindle in accordance with FIG. 6d can be carried out not by push-indevice 74, but by gripper 42".

The method will now be explained briefly with reference to the sequencein accordance with FIGS. 5 to 7 which has already been described indetail. Herein only the differences from the first embodiment will beset forth.

The illustration in FIG. 16 corresponds to the situation according toFIG. 5a. The workpiece gripper 42" is swivelled to such an extent thatgripper G₂ can grip the half-finished part Z_(h) clamped in spindle S₁in spindle position VI and remove it from it. Simultaneously, doublegripper 42" has already gripped the raw part Z_(r) in gripper G₁. Afterthe half-finished part Z_(h) has been removed from spindle S₁, gripper42" rotates through 180 degrees about the longitudinal axis 60 of arm40, as in the first embodiment in FIG. 5c. Hence the raw part Z_(r) isalready aligned coaxially with spindle S₁ and can be inserted into it inanalogy with FIG. 5e. After insertion of raw part Z_(r), the spindledrum is indexed, and so spindle S₆ carrying a finished part Z_(f) is nowstanding in spindle position VI in analogy with FIG. 6a. The now emptygripper G₁ is already aligned coaxially with the spindle S₆ now standingin spindle position VI, and so the finished part Z_(f) can be gripped inanalogy with FIG. 6b and removed from spindle S₆.

Finally, gripper 42" is to be swivelled through such an angle that thehalf-finished part Z_(h) held in gripper G₂ and already reversed isaligned coaxially with spindle S₆ and can subsequently be transferred inanalogy with FIG. 6d. As mentioned above, the transfer is not carriedout by the push-in device 74 additionally required in the firstembodiment, but directly by gripper G₂. The finished part Z_(f) can thenbe conveyed out and deposited on workpiece transporting device 44 inanalogy with the first embodiment.

What is claimed is:
 1. Multiple-spindle automatic machine tool formachining both sides of workpieces, comprising:a machine housing; aworking area within said machine housing; a spindle drum comprisingseveral spindles, said spindles facing said working area and havingspindle axes which are arranged at equal angular spacings around a drumaxis, said spindles being positionable in different spindle positionsfixedly arranged with respect to said machine housing by rotating saidspindle drum, said spindle drum being indexable in single steps forpositioning each spindle in the subsequent spindle position, saidspindles being designed as successive first and second spindles forclamping the workpieces on a first or second clamping side,respectively, at least one of said spindle positions being selected tobe used for feeding of raw workpieces to said spindles, removal of afinished workpiece from said spindles and changing over a half-finishedworkpiece from a first spindle to a second spindle by turning itsclamping side, said respective spindle in said selected spindle positionbeing a selected spindle; at least one feeding means for delivering rawworkpieces to said selected spindle position; at least one conveyingaway means for conveying finished workpieces away from said selectedspindle position; at least one workpiece holding device facing saidworking area and being arranged opposite said selected spindle in saidat least one selected spindle position; at least one workpiece grippingdevice being movable into a workpiece gripping position facing saidselected spindle in said at least one selected spindle position forfeeding or removing workpieces from said selected spindle, and into aworkpiece changing position facing said workpiece holding device forexchanging said half-finished workpiece with said workpiece holdingdevice; and means for controlling said machine tool, comprising:loadingmode means for feeding a raw workpiece to said one of said firstspindles in said at least one selected spindle position; changing overmode means for removing a half-finished workpiece from said firstspindle in said at least one selected spindle position and for turningsaid workpiece around from said first clamping side to said secondclamping side with said workpiece gripping device in cooperation withsaid workpiece holding device, said changing over mode means further forindexing said spindle drum by bringing one of said second spindles intosaid at least one selected spindle position and by reinserting saidhalf-finished workpiece with said second clamping side in said secondspindle in at least one selected spindle position; andunloading modemeans for conveying said finished workpiece away from said secondspindle in said at least one selected spindle position.
 2. Machine toolaccording to claim 1, wherein said workpiece gripping device comprises aworkpiece gripper rotatable about an axis extending transversely to thespindle axis.
 3. Machine tool according to claim 2, wherein a workingarea is so designed that the workpiece gripper is rotatable with atleast one workpiece gripped in it about said axis extending transverselyto said spindle axis.
 4. Machine tool according to claim 2, wherein saidworkpiece gripping device comprises a double gripper.
 5. Machine toolaccording to claim 1, wherein said workpiece gripping device isimmobilizable in at least two positions having the gripped workpieceoriented parallel to the spindle axis and arranged in rotated relationto each other through a rotary angle of 180 degrees with respect to saidaxis extending transversely to said spindle axis.
 6. Machine toolaccording to claim 5, wherein said workpiece gripping device comprisesan arm which carries a workpiece gripper and is rotatable about itslongitudinal axis.
 7. Machine tool according to claim 5, wherein saidworkpiece gripping device is movable parallel to the axis of rotation ofsaid selected spindle.
 8. Machine tool according to claim 1, whereinsaid workpiece gripping device is pivotable about a swivel axisapproximately parallel to said selected spindle axis.
 9. Machine toolaccording to claim 1, wherein said workpiece holding device is arrangedcoaxially with said selected spindle.
 10. Machine tool according toclaim 9, wherein the workpiece holding device is movable back and forthin the direction towards said selected spindle.
 11. Machine toolaccording to claim 1, wherein said workpiece gripping device representssaid conveying away means and said unloading mode means controls saidworkpiece gripping device for transferring said finished workpiece fromsaid second spindle in said at least one selected spindle position to aremoving position.
 12. Machine tool according to claim 1, wherein saidworkpiece gripping device represents said feeding means and said loadingmode means controls said workpiece gripping device for transferring araw workpiece from a feeding position to said first spindle in said atleast one selected spindle position.
 13. Machine tool according to claim1, wherein said feeding means is designed for feeding a raw workpiececoaxially with said first spindles.
 14. Machine tool according to claim13, wherein said feeding means is a bar stock feeding means for feedingsaid raw workpiece in the form of a bar.
 15. Machine tool according toclaim 14, wherein said changing over mode means comprise cut-off modemeans for controlling a cutting off of said half-finished workpiece insaid selected spindle position for removing said half-finished workpiecefrom said first spindle in said at least one selected spindle position.16. Machine tool according to claim 15, wherein the workpiece holdingdevice is a synchronous spindle arranged coaxially with said selectedspindle.
 17. Machine tool according to claim 16, wherein saidsynchronous spindle is movable back and forth in the direction towardssaid selected spindle.
 18. Machine tool according to claim 13, whereinsaid workpiece gripping device represents said conveying away means andsaid unloading mode means controls said workpiece gripping device fortransferring said finished workpiece from said second spindle in said atleast one selected spindle position to a removing position. 19.Multiple-spindle automatic machine tool for machining both sides ofworkpieces, comprising:a machine housing; a working area within saidmachine housing; a spindle drum comprising several spindles, saidspindles facing said working area and having spindle axes which arearranged at equal angular spacings around a drum axis, said spindlesbeing positionable in different spindle positions fixedly arranged withrespect to said machine housing by rotating said spindle drum, saidspindle drum being indexable in single steps for positioning eachspindle in the subsequent spindle position, said spindles being designedas successive first and second spindles for clamping the workpieces on afirst or second clamping side, respectively, at least one of saidspindle positions being selected to be used for feeding of rawworkpieces to said spindles, removal of finished workpieces from saidspindles and changing over of half-finished workpieces from a firstspindle to a second spindle, said respective spindle in said selectedspindle position being a selected spindle; at least one feeding meansfor delivering raw workpieces to said selected spindle position; atleast one conveying away means for conveying finished workpieces awayfrom said selected spindle position; at least one workpiece grippingdevice, said gripping device being rotatable about an axis perpendicularto said spindle axis of said selected spindle through an angle ofrotation of 180 degrees for changing the clamping side of the workpiece,said gripping device being further movable into a workpiece grippingposition facing said selected spindle in said selected spindle positionfor feeding or removing workpieces from said selected spindle; means forcontrolling said machine tool, comprising:loading mode means for feedinga raw workpiece to said one of said first spindles in said at least oneselected spindle position; changing over mode means using said workpiecegripping device for removing a half-finished workpiece from said firstspindle in said at least one selected spindle position, for turning saidworkpiece round from said first clamping side to said second clampingside, for indexing said spindle drum bringing one of said secondspindles into said at least one selected spindle position, and forreinserting said half-finished workpiece with said second clamping sidein said second spindle in said at least one selected spindle position;and unloading mode means for conveying said finished workpiece away fromsaid second spindle in said at least one selected spindle position. 20.Machine tool according to claim 19, wherein said working area is sodesigned that the workpiece gripper is rotatable with at least oneworkpiece gripped in it about the axis extending transversely to thespindle axis.
 21. Machine tool according to claim 19, wherein saidworkpiece gripping device comprises an arm which carries the workpiecegripping device and is rotatable about its longitudinal axis. 22.Machine tool according to claim 19, wherein said workpiece grippingdevice is a double gripper.
 23. Machine tool according to claim 19,wherein said workpiece gripping device is movable parallel to axes ofrotation of the spindles.
 24. Machine tool according to claim 19,wherein said workpiece gripping device is pivotable about a swivel axisapproximately parallel to the spindle axis.
 25. Machine tool accordingto claim 19, wherein said workpiece gripping device is a radial gripper.26. Machine tool according to claim 19, wherein said workpiece grippingdevice represents said conveying away means and said unloading modemeans controls said workpiece gripping device for transferring saidfinished workpiece from said second spindle in said at least oneselected spindle position to a removing position.
 27. Machine toolaccording to claim 19, wherein said workpiece gripping device representssaid feeding means and said loading mode means controls said workpiecegripping device for transferring a raw workpiece from a feeding positionto said first spindle in said at least one selected spindle position.28. Machine tool according to claim 19, wherein said feeding means isdesigned for feeding a raw workpiece coaxially with said first spindles.29. Machine tool according to claim 28, wherein said workpiece grippingdevice represents said conveying away means and said unloading modemeans controls said workpiece gripping device for transferring saidfinished workpiece from said second spindle in said at least oneselected spindle position to a removing position.
 30. Machine toolaccording to claim 28, wherein said feeding means is a bar stock feedingmeans for feeding said raw workpiece in the form of a bar.
 31. Machinetool according to claim 30, w herein said changing over mode meanscomprise cut-off mode means for controlling a cutting off of saidhalf-finished workpiece in said selected spindle position for removingsaid half-finished workpiece from said first spindle in said at leastone selected spindle position.
 32. Machine tool according to claim 30,wherein said workpiece gripping device comprises a stop surface servingas delimitation for advance of bar stock.
 33. Machine tool according toclaim 32, wherein said workpiece gripping device is provided with asensor which reports contact with the stop surface.
 34. Multiple-spindleautomatic machine tool for machining both sides of workpieces,comprising:a machine housing; a working area within said machinehousing; a spindle drum comprising several spindles, said spindlesfacing said working area and having spindle axes which are parallel toeach other and are arranged at equal angular spacings around a drumaxis, said spindles being positionable in different spindle positionsfixedly arranged with respect to said machine housing by rotting saidspindle drum, said spindle drum being indexable in single steps forpositioning each spindle in the subsequent spindle position, saidspindles being designed as successive first and second spindles forclamping the workpieces on a first or second clamping side,respectively, two of said spindle positions being selected, each beingused for feeding of raw workpieces to said spindles, removal of finishedworkpieces from said spindles and changing over of half-finishedworkpieces from a first spindle to a second spindle, said respectivespindle in said selected spindle position being a selected spindle; afeeding means for being associated with said selected spindle positionsfor delivering raw workpieces to each of said selected spindlepositions; a conveying away means being associated with said selectedspindle positions for conveying finished workpieces away from each ofsaid selected spindle positions; a workpiece gripping device beingassociated with said selected spindle positions being movable into aworkpiece gripping position facing said selected spindle in saidselected spindle position for feeding or removing workpieces from saidselected spindle, and into a workpiece changing position for changingthe clamping side of said workpiece; and means for controlling saidmachine tool, comprising:loading mode means for each of said selectedspindle positions for feeding a raw workpiece to said one of said firstspindles in said at least one selected spindle position; changing overmode means for each of said selected spindle positions by removing ahalf-finished workpiece from said first spindle in said at least oneselected spindle position, by turning said workpiece round from saidfirst clamping side to said second clamping side, by indexing saidspindle drum bringing one of said second spindles into said at least oneselected spindle position, and by inserting said half-finished workpiecewith said second clamping side in said second spindle in said at leastone selected spindle position; and unloading mode means for each of saidselected spindle positions conveying a finished workpiece away from saidsecond spindle in said at least one selected spindle position. 35.Machine tool according to claim 34, wherein said selected spindlepositions are arranged opposite each other.
 36. Machine tool accordingto claim 34 further comprising at least one workpiece holding deviceassociated with each of said selected spindle positions and facing saidworking area and being arranged opposite said selected spindle in saidrespective selected spindle position and having each of said workpiecegripping devices designed to be movable into a workpiece changingposition facing said respective workpiece holding device for exchanginga workpiece with said respective workpiece holding device.
 37. Machinetool according to claim 34, wherein each workpiece gripping devicecomprises a workpiece gripper rotatable about an axis extendingtransversely to the spindle axis.
 38. Machine tool according to claim37, wherein said workpiece gripper is a double gripper.
 39. Machine toolaccording to claim 34, wherein each workpiece gripping device is movableparallel to axes of rotation of said selected spindles.
 40. Machine toolaccording to claim 36, wherein each workpiece holding device is arrangedcoaxially with the selected spindle.
 41. Machine tool according to claim40, wherein said workpiece holding device is movable to and fro in thedirection towards the associated spindle.
 42. Machine tool according toclaim 34, wherein said workpiece gripping device represents saidconveying away means and said loading mode means controls said workpiecegripping device for transferring said finished workpiece from saidsecond spindle in said at least one selected spindle position to aremoving position.
 43. Machine tool according to claim 34, wherein saidworkpiece gripping device represents said feeding means and said loadingmode means controls said workpiece gripping device for transferring araw workpiece from a feeding position to said first spindle in said atleast one selected spindle position.
 44. Machine tool according to claim34, wherein said feeding means is designed for feeding a raw workpiececoaxially with said first spindles.
 45. Machine tool according to claim34, wherein said feeding means is a bar stock feeding means for feedingsaid raw workpiece in the form of a bar.
 46. Machine tool according toclaim 45, wherein said changing over mode means comprise cut-off modemeans for controlling a cutting off of said half-finished workpiece insaid selected spindle position for removing said half-finished workpiecefrom said first spindle in said at least one selected spindle position.47. Machine tool according to claim 46, wherein said workpiece holdingdevice is a synchronous spindle.
 48. Machine tool according to claim 44,wherein said workpiece gripping device represent said conveying awaymeans and said unloading mode means controls said workpiece grippingdevice for transferring said finished workpiece from said second spindlein said at least one selected spindle position to a removing position.